Recent studies have proved the usefulness of macroscopic surface patterning for the improvement of tribological performances of sliding contacts [1-2]. The effects of scaling down the texturing dimensions to the nanoscale have not yet been investigated to a comparable extent.
By means of classical Molecular Dynamics simulations we show that the sliding frictional properties of a thin lubricant film are significantly affected by the presence of nanoscale superficial patterning of the moving confining walls [3], leading to suppression of the stick-slip regime and reduction of friction. We study a 2-dimensional system consisting of a rigid, patterned substrate (to simulate the texturing of experimental surfaces), a rigid layer (mimicking the driven top wall) and a confined lubricant in between. In particular we investigate the friction and the tribological response when the top layer is pulled at constant velocity by an attached spring. In absence of surface patterning, for suitable applied load and temperatures, due to the effect of confinement, we observe the layering of the lubricant film which then tends to solidify [4-7]. In this situation (and for not too high external driving), friction becomes significant due to the occurrence of the so-called stick-slip regime. This behavior disappears only at very high temperatures. On the contrary in the presence of
surface patterning, and under the same operative conditions, our numerical simulations show a drastic reduction of sliding friction. This decrease is ascribed to a local melting of the film nearby the surface grooves (reduced effect of the confinement) and to a 'pattern-increased' interlayer diffusion in the lubricant film. We believe these findings to be relevant for nanotechnology applications.
References :
|1| U. Pettersson et al. , Tribol. Lett. 17, 553 (2004)
|2| A. Blatter et al. , Tribol. Lett. 4, 237 (1998)
|3| C. Cottin-Bizonne et al. , Nature Materials 2, 237 (2003)
|4| J. Klein et al., J. Chem. Phys., 108, 16, 6996 (1998)
|5| A. Weinstein et al., Europhys. Lett. 42, 61 (1998)
|6| O.M. Braun et al. , Phys. Rev. E 63, 046110 (2001)
|7| O.M. Braun et al. , Phys. Rev. E 68, 011506 (2003)
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